Patrick Barkham

Genome study finds the invasive clonal freshwater crayfish is descended from a single female and reproduces without males

The marbled crayfish threatens to crowd out seven native species in Madagascar. Photograph: Ranja Andriantsoa/Nature

A voracious pest that mutated in a German aquarium and is marching around the world without the need for sexual reproduction may sound like science fiction, but a genetic study has revealed that a rapidly spreading all-female army of crayfish is descended from a single female and reproduces without any males.

The clonal freshwater crayfish is regarded as an invasive species which threatens endemic wild species, but its success may help scientists better understand how cancer spreads.

Researchers have been surprised by the marbled crayfish’s reproductive success and remarkable adaptability, with genetically identical crayfish now thriving in the wild in diverse habitats from subtropical Madagascar to Sweden, Japan and German cities including Hanover and Heidelberg.

Scientists from the German Cancer Research Center used genome sequencing and comparative studies of individual animals to prove that the all-female offspring of the marbled crayfish are genetically identical, in a study published in Nature, Ecology & Evolution.

Previous genetic studies have shown that the marbled crayfish (Procambarus virginalis) recently split from the slough crayfish (Procambarus fallax), found in the wild in Everglades national park in Florida.

The new species was first identified in a German aquarium in 1995 but has since spread around the world – with a helping hand from humans.

“It was known that the crayfish can establish itself in the wild after releases from the aquarium,” said Frank Lyko of the German Cancer Research Center. “But the news was that it can spread so rapidly and massively.”

In another part of the study, a scientist in Madagascar examined how well the crayfish is able to multiply in the wild via parthenogenesis, a natural form of asexual reproduction.

The crayfish, now banned in the European Union, has been distributed by the aquarium trade and has rapidly spread across Madagascar in less than a decade because of its popularity as a cheap source of protein for humans. According to Lyko, the marbled crayfish could out-compete seven native crayfish.

But researchers hope that the adaptability of the clonal crayfish may also shed light on how cancer tumours adapt to their environment by developing resistance against drug treatments, for instance.

The team led by Lyko wants to look more closely at how clonal evolution occurs in both marbled crayfish and tumours. “Epigenetic mechanisms”, which work like switches turning genes on or off, enable both the crayfish and tumours to adapt to a wide variety of habitats.

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